Recently, a display device comprising a thin-film transistor has been put into practical use. Examples of the display device include a liquid crystal display device, an organic electroluminescence (EL) display device, etc. In such a thin-film transistor, a leakage current is produced by a semiconductor layer irradiated with light and an operation error may be thereby caused. For this reason, technology of providing a light-shielding film for shielding the semiconductor layer from the light has been proposed. A parasitic capacitance is produced between the light-shielding film and the semiconductor layer. As the area of the light-shielding film opposed to the semiconductor layer is larger, the parasitic capacitance becomes greater. In general, a comparatively great parasitic capacitance is produced since the light-shielding film is opposed to a substantially entire body of the semiconductor layer.
It should be noted that, in the thin-film transistor disposed in the vicinity of an intersection portion of a gate line and a source line, the potential of the semiconductor layer on a side electrically connected to the source line is varied in accordance with a video signal supplied to the source line, in a layout in which at least a part of the semiconductor layer overlaps the source line. For this reason, the potential of the light-shielding film which is capacitively coupled to the semiconductor layer is varied in accordance with the video signal. In addition, the light-shielding film is also opposed to the semiconductor layer on a side electrically connected to the pixel electrode. For this reason, the pixel potential written and held in the pixel electrode becomes unstable because of potential variation of the light-shielding film. Thus, in each of pixels electrically connected to the same source line, the held pixel potential may be disturbed in accordance with the video signal supplied to the source line and the display quality may be deteriorated.